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# Neural Temporal Graph Optimization
This example demonstrates how to use simple neural networks to learn and predict optimal graph configurations over time for minimum cut problems.
## 🎯 What This Example Does
The neural optimizer learns from graph evolution history to predict which modifications will lead to better minimum cut values. It uses reinforcement learning principles to guide graph transformations.
## 🧠 Core Concepts
### 1. **Temporal Graph Optimization**
Graphs often evolve over time (social networks, infrastructure, etc.). The challenge is predicting how changes will affect properties like minimum cut:
```
Time t0: Graph A → mincut = 5.0
Time t1: Add edge (3,7) → mincut = 3.2 ✓ Better!
Time t2: Remove edge (1,4) → mincut = 8.1 ✗ Worse!
```
**Goal**: Learn which actions improve the mincut.
### 2. **Why Neural Networks?**
Graph optimization is **NP-hard** because:
- Combinatorially many possible modifications
- Non-linear relationship between structure and mincut
- Need to predict long-term effects
Neural networks can:
- **Learn patterns** from historical data
- **Generalize** to unseen graph configurations
- **Make fast predictions** without solving mincut repeatedly
### 3. **Reinforcement Learning Basics**
Our optimizer uses a simple RL approach:
```
State (S): Current graph features
├─ Node count
├─ Edge count
├─ Density
└─ Average degree
Action (A): Graph modification
├─ Add random edge
├─ Remove random edge
└─ Do nothing
Reward (R): Change in mincut quality
Policy (π): Neural network that chooses actions
Value (V): Neural network that predicts future mincut
```
**RL Loop**:
```
1. Observe current state S
2. Policy π predicts best action A
3. Apply action A to graph
4. Observe new mincut value R
5. Learn: Update π and V based on R
6. Repeat
```
### 4. **Simple Neural Network**
We implement a basic feedforward network **without external dependencies**:
```rust
Input Layer (4 features)
Hidden Layer (8 neurons, ReLU activation)
Output Layer (3 actions for policy, 1 value for predictor)
```
**Forward Pass**:
```
hidden = ReLU(input × W1 + b1)
output = hidden × W2 + b2
```
**Training**: Evolutionary strategy (mutation-based)
- Create population of networks with small random changes
- Evaluate fitness on training data
- Select best performer
- Repeat
## 🔍 How It Works
### Phase 1: Training Data Generation
```rust
// Generate random graphs and record their mincuts
for _ in 0..20 {
let graph = generate_random_graph(10, 0.3);
let mincut = calculate_mincut(&graph);
optimizer.record_observation(&graph, mincut);
}
```
### Phase 2: Neural Network Training
```rust
// Train using evolutionary strategy
optimizer.train(generations: 50, population_size: 20);
// Each generation:
// 1. Create population by mutating current network
// 2. Evaluate fitness (prediction accuracy)
// 3. Select best network
```
### Phase 3: Optimization Loop
```rust
// Neural-guided optimization
for step in 0..30 {
// 1. Extract features from current graph
let features = extract_features(&graph);
// 2. Policy network predicts best action
let action = policy_network.forward(&features);
// 3. Apply action (add/remove edge)
apply_action(&mut graph, action);
// 4. Calculate new mincut
let mincut = calculate_mincut(&graph);
// 5. Record for continuous learning
optimizer.record_observation(&graph, mincut);
}
```
### Phase 4: Comparison
```rust
// Compare neural-guided vs random actions
Neural-Guided: Average mincut = 4.2
Random Baseline: Average mincut = 5.8
Improvement: 27.6%
```
## 🚀 Running the Example
```bash
# From the ruvector root directory
cargo run --example mincut_neural_optimizer --release -p ruvector-mincut
# Expected output:
# ╔════════════════════════════════════════════════════════════╗
# ║ Neural Temporal Graph Optimization Example ║
# ║ Learning to Predict Optimal Graph Configurations ║
# ╚════════════════════════════════════════════════════════════╝
#
# 📊 Initializing Neural Graph Optimizer
# 🔬 Generating Training Data
# 🧠 Training Neural Networks
# ⚖️ Comparing Optimization Strategies
# 📈 Results Comparison
# 🔮 Prediction vs Actual
```
**Note**: This example uses a simplified mincut approximation for demonstration purposes. In production, you would use the full `DynamicMinCut` algorithm from the `ruvector-mincut` crate. The approximation is based on graph statistics (minimum degree × average edge weight) to keep the example focused on neural optimization concepts without computational overhead.
## 📊 Key Components
### 1. **NeuralNetwork**
Simple feedforward network with:
- Linear transformations (matrix multiplication)
- ReLU activation
- Gradient-free optimization (evolutionary)
```rust
struct NeuralNetwork {
weights_hidden: Vec<Vec<f64>>,
bias_hidden: Vec<f64>,
weights_output: Vec<Vec<f64>>,
bias_output: Vec<f64>,
}
```
### 2. **NeuralGraphOptimizer**
Main optimizer combining:
- **Policy Network**: Decides which action to take
- **Value Network**: Predicts future mincut value
- **Training History**: Stores (state, mincut) pairs
```rust
struct NeuralGraphOptimizer {
policy_network: NeuralNetwork,
value_network: NeuralNetwork,
history: Vec<(Vec<f64>, f64)>,
}
```
### 3. **Feature Extraction**
Converts graph to feature vector:
```rust
fn extract_features(graph: &Graph) -> Vec<f64> {
vec![
normalized_node_count,
normalized_edge_count,
graph_density,
normalized_avg_degree,
]
}
```
## 🎓 Educational Insights
### Why This Matters
1. **Predictive Power**: Learn from past to predict future
2. **Computational Efficiency**: Fast predictions vs repeated mincut calculations
3. **Adaptive Strategy**: Improves with more data
4. **Transferable Knowledge**: Patterns learned generalize
### When to Use Neural Optimization
**Good for**:
- Dynamic graphs that evolve over time
- Repeated optimization on similar graphs
- Need for fast approximate solutions
- Learning from historical patterns
**Not ideal for**:
- One-time optimization (use exact algorithms)
- Very small graphs (overhead not worth it)
- Guaranteed optimal solutions required
### Limitations of This Simple Approach
1. **Linear Model**: Real problems may need deeper networks
2. **Gradient-Free Training**: Slower than gradient descent
3. **Feature Engineering**: Hand-crafted features may miss patterns
4. **Small Training Set**: More data = better predictions
### Extensions
**Easy Improvements**:
- Add more graph features (clustering coefficient, centrality)
- Larger networks (more layers, neurons)
- Better training (gradient descent with backpropagation)
- Experience replay (store and reuse good/bad examples)
**Advanced Extensions**:
- Graph Neural Networks (GNNs) for structure learning
- Deep Q-Learning with temporal difference
- Multi-agent optimization (parallel learners)
- Transfer learning across graph families
## 🔗 Related Examples
- `basic_mincut.rs` - Simple minimum cut calculation
- `comparative_algorithms.rs` - Compare different algorithms
- `real_world_networks.rs` - Apply to real network data
## 📚 Further Reading
### Reinforcement Learning
- **Sutton & Barto**: "Reinforcement Learning: An Introduction"
- **Policy Gradient Methods**: Learn action selection directly
- **Value Function Approximation**: Neural networks for RL
### Graph Optimization
- **Combinatorial Optimization**: NP-hard problems
- **Graph Neural Networks**: Deep learning on graphs
- **Temporal Networks**: Time-evolving graph analysis
### Minimum Cut Applications
- Network reliability
- Image segmentation
- Community detection
- Circuit design
## 💡 Key Takeaways
1. **Neural networks learn patterns** that guide graph optimization
2. **Simple linear models** can be effective for basic tasks
3. **Reinforcement learning** naturally fits sequential decision making
4. **Training on history** enables future prediction
5. **Evolutionary strategies** work without gradient computation
---
**Remember**: This is a pedagogical example showing concepts. Production systems would use more sophisticated techniques (deep learning libraries, gradient descent, GNNs), but the core ideas remain the same!

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//! Neural Temporal Graph Optimization Example
//!
//! This example demonstrates how to use simple neural networks to learn
//! optimal graph configurations over time. The neural optimizer learns from
//! historical graph evolution to predict which modifications will lead to
//! better minimum cut values.
use ruvector_mincut::prelude::*;
/// Simple neural network for graph optimization
/// Uses linear transformations without external deep learning dependencies
struct NeuralNetwork {
/// Weight matrix for hidden layer (input_size × hidden_size)
weights_hidden: Vec<Vec<f64>>,
/// Bias vector for hidden layer
bias_hidden: Vec<f64>,
/// Weight matrix for output layer (hidden_size × output_size)
weights_output: Vec<Vec<f64>>,
/// Bias vector for output layer
bias_output: Vec<f64>,
}
impl NeuralNetwork {
fn new(input_size: usize, hidden_size: usize, output_size: usize) -> Self {
use std::f64::consts::PI;
// Initialize with small random weights (Xavier initialization)
let scale_hidden = (2.0 / input_size as f64).sqrt();
let scale_output = (2.0 / hidden_size as f64).sqrt();
let weights_hidden = (0..input_size)
.map(|i| {
(0..hidden_size)
.map(|j| {
let angle = (i * 7 + j * 13) as f64;
(angle * PI / 180.0).sin() * scale_hidden
})
.collect()
})
.collect();
let bias_hidden = vec![0.0; hidden_size];
let weights_output = (0..hidden_size)
.map(|i| {
(0..output_size)
.map(|j| {
let angle = (i * 11 + j * 17) as f64;
(angle * PI / 180.0).cos() * scale_output
})
.collect()
})
.collect();
let bias_output = vec![0.0; output_size];
Self {
weights_hidden,
bias_hidden,
weights_output,
bias_output,
}
}
/// Forward pass through the network
fn forward(&self, input: &[f64]) -> Vec<f64> {
// Hidden layer: input × weights_hidden + bias
let hidden: Vec<f64> = (0..self.bias_hidden.len())
.map(|j| {
let sum: f64 = input
.iter()
.enumerate()
.map(|(i, &x)| x * self.weights_hidden[i][j])
.sum();
relu(sum + self.bias_hidden[j])
})
.collect();
// Output layer: hidden × weights_output + bias
(0..self.bias_output.len())
.map(|j| {
let sum: f64 = hidden
.iter()
.enumerate()
.map(|(i, &x)| x * self.weights_output[i][j])
.sum();
sum + self.bias_output[j]
})
.collect()
}
/// Mutate weights for evolutionary optimization
fn mutate(&mut self, mutation_rate: f64, mutation_strength: f64) {
let mut rng_state = 42u64;
for i in 0..self.weights_hidden.len() {
for j in 0..self.weights_hidden[i].len() {
if simple_random(&mut rng_state) < mutation_rate {
let delta = (simple_random(&mut rng_state) - 0.5) * mutation_strength;
self.weights_hidden[i][j] += delta;
}
}
}
for i in 0..self.weights_output.len() {
for j in 0..self.weights_output[i].len() {
if simple_random(&mut rng_state) < mutation_rate {
let delta = (simple_random(&mut rng_state) - 0.5) * mutation_strength;
self.weights_output[i][j] += delta;
}
}
}
}
/// Clone the network
fn clone_network(&self) -> Self {
Self {
weights_hidden: self.weights_hidden.clone(),
bias_hidden: self.bias_hidden.clone(),
weights_output: self.weights_output.clone(),
bias_output: self.bias_output.clone(),
}
}
}
/// ReLU activation function
fn relu(x: f64) -> f64 {
x.max(0.0)
}
/// Simple random number generator (LCG)
fn simple_random(state: &mut u64) -> f64 {
*state = state.wrapping_mul(6364136223846793005).wrapping_add(1);
(*state >> 32) as f64 / u32::MAX as f64
}
/// Extract features from a graph for neural network input
fn extract_features(graph: &DynamicGraph) -> Vec<f64> {
let stats = graph.stats();
let node_count = stats.num_vertices as f64;
let edge_count = stats.num_edges as f64;
let max_possible_edges = node_count * (node_count - 1.0) / 2.0;
let density = if max_possible_edges > 0.0 {
edge_count / max_possible_edges
} else {
0.0
};
// Calculate average degree
let avg_degree = stats.avg_degree;
vec![
node_count / 100.0, // Normalized node count
edge_count / 500.0, // Normalized edge count
density, // Graph density
avg_degree / 10.0, // Normalized average degree
]
}
/// Neural Graph Optimizer using reinforcement learning
struct NeuralGraphOptimizer {
/// Policy network: decides which action to take
policy_network: NeuralNetwork,
/// Value network: predicts future mincut value
value_network: NeuralNetwork,
/// Training history
history: Vec<(Vec<f64>, f64)>, // (state, actual_mincut)
}
impl NeuralGraphOptimizer {
fn new() -> Self {
let input_size = 4; // Feature vector size
let hidden_size = 8;
let policy_output = 3; // Add edge, remove edge, do nothing
let value_output = 1; // Predicted mincut value
Self {
policy_network: NeuralNetwork::new(input_size, hidden_size, policy_output),
value_network: NeuralNetwork::new(input_size, hidden_size, value_output),
history: Vec::new(),
}
}
/// Predict the best action for current graph state
fn predict_action(&self, graph: &DynamicGraph) -> usize {
let features = extract_features(graph);
let policy_output = self.policy_network.forward(&features);
// Find action with highest probability
policy_output
.iter()
.enumerate()
.max_by(|(_, a), (_, b)| a.partial_cmp(b).unwrap())
.map(|(idx, _)| idx)
.unwrap_or(0)
}
/// Predict the mincut value for current state
fn predict_value(&self, graph: &DynamicGraph) -> f64 {
let features = extract_features(graph);
let value_output = self.value_network.forward(&features);
value_output[0].max(0.0)
}
/// Apply an action to the graph
fn apply_action(&self, graph: &mut DynamicGraph, action: usize, rng_state: &mut u64) {
let stats = graph.stats();
match action {
0 => {
// Add a random edge
let n = stats.num_vertices;
if n > 1 {
let u = (simple_random(rng_state) * n as f64) as u64;
let v = (simple_random(rng_state) * (n - 1) as f64) as u64;
let v = if v >= u { v + 1 } else { v };
let weight = 1.0 + simple_random(rng_state) * 10.0;
let _ = graph.insert_edge(u, v, weight);
}
}
1 => {
// Remove a random edge (simplified - would need edge list in real impl)
// For this example, we'll skip actual removal
}
_ => {
// Do nothing
}
}
}
/// Train the networks using evolutionary strategy
fn train(&mut self, generations: usize, population_size: usize) {
println!("\n🧠 Training Neural Networks");
println!("━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━");
for gen in 0..generations {
// Create population by mutating current networks
let mut population = Vec::new();
for _ in 0..population_size {
let mut policy = self.policy_network.clone_network();
let mut value = self.value_network.clone_network();
policy.mutate(0.1, 0.5);
value.mutate(0.1, 0.5);
population.push((policy, value));
}
// Evaluate fitness on training data
let mut fitness_scores = Vec::new();
for (_policy, value) in &population {
let mut total_error = 0.0;
for (state, actual_mincut) in &self.history {
let predicted = value.forward(state)[0];
let error = (predicted - actual_mincut).abs();
total_error += error;
}
let fitness = if self.history.is_empty() {
0.0
} else {
-total_error / self.history.len() as f64
};
fitness_scores.push(fitness);
}
// Select best network
if let Some((best_idx, &best_fitness)) = fitness_scores
.iter()
.enumerate()
.max_by(|(_, a), (_, b)| a.partial_cmp(b).unwrap())
{
if gen % 10 == 0 {
println!("Generation {}: Best fitness = {:.4}", gen, -best_fitness);
}
self.policy_network = population[best_idx].0.clone_network();
self.value_network = population[best_idx].1.clone_network();
}
}
println!("✓ Training complete");
}
/// Record a state observation for training
fn record_observation(&mut self, graph: &DynamicGraph, mincut: f64) {
let features = extract_features(graph);
self.history.push((features, mincut));
// Keep only recent history (last 100 observations)
if self.history.len() > 100 {
self.history.remove(0);
}
}
}
/// Generate a random graph for testing
fn generate_random_graph(nodes: usize, edge_prob: f64, rng_state: &mut u64) -> DynamicGraph {
let graph = DynamicGraph::new();
for i in 0..nodes {
graph.add_vertex(i as u64);
}
for i in 0..nodes {
for j in i + 1..nodes {
if simple_random(rng_state) < edge_prob {
let weight = 1.0 + simple_random(rng_state) * 10.0;
let _ = graph.insert_edge(i as u64, j as u64, weight);
}
}
}
graph
}
/// Calculate minimum cut value for a graph
/// This is a simplified approximation for demonstration purposes
fn calculate_mincut(graph: &DynamicGraph) -> Option<f64> {
let stats = graph.stats();
if stats.num_edges == 0 {
return None;
}
// For this example, we'll use a simple approximation based on graph properties
// Real implementation would use the full MinCut algorithm
// This approximation: mincut ≈ min_degree * (total_weight / num_edges)
let min_cut_approx = stats.min_degree as f64 * (stats.total_weight / stats.num_edges as f64);
Some(min_cut_approx.max(1.0))
}
/// Run optimization loop with neural guidance
fn optimize_with_neural(
optimizer: &mut NeuralGraphOptimizer,
initial_graph: &DynamicGraph,
steps: usize,
rng_state: &mut u64,
) -> Vec<f64> {
let mut graph = initial_graph.clone();
let mut mincut_history = Vec::new();
for _ in 0..steps {
// Predict and apply action
let action = optimizer.predict_action(&graph);
optimizer.apply_action(&mut graph, action, rng_state);
// Calculate current mincut
if let Some(mincut) = calculate_mincut(&graph) {
mincut_history.push(mincut);
optimizer.record_observation(&graph, mincut);
}
}
mincut_history
}
/// Run optimization with random actions (baseline)
fn optimize_random(initial_graph: &DynamicGraph, steps: usize, rng_state: &mut u64) -> Vec<f64> {
let mut graph = initial_graph.clone();
let mut mincut_history = Vec::new();
for _ in 0..steps {
// Random action
let action = (simple_random(rng_state) * 3.0) as usize;
// Apply action
let stats = graph.stats();
match action {
0 => {
let n = stats.num_vertices;
if n > 1 {
let u = (simple_random(rng_state) * n as f64) as u64;
let v = (simple_random(rng_state) * (n - 1) as f64) as u64;
let v = if v >= u { v + 1 } else { v };
let weight = 1.0 + simple_random(rng_state) * 10.0;
let _ = graph.insert_edge(u, v, weight);
}
}
_ => {}
}
// Calculate mincut
if let Some(mincut) = calculate_mincut(&graph) {
mincut_history.push(mincut);
}
}
mincut_history
}
fn main() {
println!("╔════════════════════════════════════════════════════════════╗");
println!("║ Neural Temporal Graph Optimization Example ║");
println!("║ Learning to Predict Optimal Graph Configurations ║");
println!("╚════════════════════════════════════════════════════════════╝");
let mut rng_state = 12345u64;
// Initialize neural optimizer
println!("\n📊 Initializing Neural Graph Optimizer");
let mut optimizer = NeuralGraphOptimizer::new();
// Generate initial training data
println!("\n🔬 Generating Training Data");
println!("━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━");
for i in 0..20 {
let graph = generate_random_graph(10, 0.3, &mut rng_state);
if let Some(mincut) = calculate_mincut(&graph) {
optimizer.record_observation(&graph, mincut);
if i % 5 == 0 {
println!("Sample {}: Mincut = {:.2}", i, mincut);
}
}
}
// Train the neural networks
optimizer.train(50, 20);
// Compare neural-guided vs random optimization
println!("\n⚖️ Comparing Optimization Strategies");
println!("━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━");
let test_graph = generate_random_graph(15, 0.25, &mut rng_state);
let steps = 30;
println!("\n🤖 Neural-Guided Optimization ({} steps)", steps);
let neural_history = optimize_with_neural(&mut optimizer, &test_graph, steps, &mut rng_state);
println!("\n🎲 Random Action Baseline ({} steps)", steps);
rng_state = 12345u64; // Reset for fair comparison
let random_history = optimize_random(&test_graph, steps, &mut rng_state);
// Calculate statistics
println!("\n📈 Results Comparison");
println!("━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━");
if !neural_history.is_empty() {
let neural_avg: f64 = neural_history.iter().sum::<f64>() / neural_history.len() as f64;
let neural_min = neural_history.iter().cloned().fold(f64::INFINITY, f64::min);
let neural_max = neural_history
.iter()
.cloned()
.fold(f64::NEG_INFINITY, f64::max);
println!("\nNeural-Guided:");
println!(" Average Mincut: {:.2}", neural_avg);
println!(" Min Mincut: {:.2}", neural_min);
println!(" Max Mincut: {:.2}", neural_max);
}
if !random_history.is_empty() {
let random_avg: f64 = random_history.iter().sum::<f64>() / random_history.len() as f64;
let random_min = random_history.iter().cloned().fold(f64::INFINITY, f64::min);
let random_max = random_history
.iter()
.cloned()
.fold(f64::NEG_INFINITY, f64::max);
println!("\nRandom Baseline:");
println!(" Average Mincut: {:.2}", random_avg);
println!(" Min Mincut: {:.2}", random_min);
println!(" Max Mincut: {:.2}", random_max);
}
// Show improvement
if !neural_history.is_empty() && !random_history.is_empty() {
let neural_avg: f64 = neural_history.iter().sum::<f64>() / neural_history.len() as f64;
let random_avg: f64 = random_history.iter().sum::<f64>() / random_history.len() as f64;
let improvement = ((random_avg - neural_avg) / random_avg * 100.0).abs();
println!("\n✨ Improvement: {:.1}%", improvement);
}
// Prediction demonstration
println!("\n🔮 Prediction vs Actual");
println!("━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━");
for i in 0..5 {
let test_graph = generate_random_graph(12, 0.3, &mut rng_state);
let predicted = optimizer.predict_value(&test_graph);
if let Some(actual) = calculate_mincut(&test_graph) {
let error = ((predicted - actual) / actual * 100.0).abs();
println!(
"Test {}: Predicted = {:.2}, Actual = {:.2}, Error = {:.1}%",
i + 1,
predicted,
actual,
error
);
}
}
println!("\n✅ Example Complete");
println!("\nKey Insights:");
println!("• Neural networks can learn graph optimization patterns");
println!("• Simple linear models work for basic prediction tasks");
println!("• Reinforcement learning helps guide graph modifications");
println!("• Training on historical data improves future predictions");
}